Conventionally known Kr85 leak testing can be utilized for a leak test up to 10−13 Pam3/s, but cannot be used in any mass-production machine because radioactive isotopes are used.
Further, for an MEMS package, a test of an ultra-fine leak of 10−13 Pam3/s or less is required. However, an existing technology is not applicable for a highly reliable calibration, and there is not any standard (reference) for calibration.
For example, in PTL1, there is described a leak gas measuring device which uses a cryopump to measure a fine leak rate from an inspection object filled with helium gas. However, this device is not provided with any calibration means.
Additionally, as a national standard of a leak rate in helium leak testing, 10−10 Pam3/s of National Institute of Standards and Technology (NIST) is minimum. A helium reference leak having a leak rate of 10−11 Pam3/s by extrapolation of this standard is sold from U.S. corporations or the like. Therefore, measurement in the range of 10−10 Pam3/s to 10−11 Pam3/s or less in helium leak testing is an extrapolation value, and has a low reliability.
In addition, at present, a calibrated helium standard leak is attached to a helium leak testing device. However, since one-point calibration is performed, a linearity of a measuring unit cannot be confirmed.
On the other hand, the present inventors have previously filed applications relating to a calibration method and a calibration device of a microporous filter for standard mixed gas leak (PTL2) and to a reference minute gas flow rate introduction device using a microporous filter (PTL3), concerning the microporous filter which becomes a molecular flow.